Face masks have long been used to administer air, oxygen or other gases to patients for various purposes, such as administering anesthesia, providing oxygen delivery for critical patients, and counteracting sleep apnea. The face masks are connected with tubes or hoses to a pressurized source of air or other breathing gases. A vent tube is usually provided to connect the face mask with the hose to supply the air to the mask. The face masks have a seal roughly contoured to match a typical human face. The mask is usually held in place against the patient's face by headgear including adjustable straps that extend around the patient's head and force the mask into a sealing engagement with the patient's face.
One of the problems with current breathing face masks is that under certain conditions it is difficult to maintain the seal between the mask and the patient's face, particularly when the patient is moving his head. Normal sleep patterns usually include some head movement, whereas the air supply hose extends from the air source at a fixed location. The lateral stress applied to the mask caused by relative movement between the patient's head and the air supply hose can easily break the seal to the patient's face, thereby defeating the goal of supplying the air or other breathing gases into the patient's respiratory system.
Efforts to provide the masks with a more reliable connection seal to the patient's face have resulted in the development of a swivel connection to prevent twisting of the air hose. Another advance in masks is to use a short vent tube having a right angle bend to minimize lateral stresses on the mask generated by movement of the patient's head relative to the air hose. The short vent tube has a reduced moment arm of bending when compared with vent tubes extending straight away from the face. Angled vent tubes are shown in U.S. Pat. No. 5,492,116 to Scarberry at al., for example. In spite of these improvements, however, there is still a great need for respiratory masks enabling more secure connections with the patient's face to prevent the loss of the seal.
Another problem with current breathing face masks is that they are uncomfortable to wear. To maintain a good seal the mask must be pressed against the patient's face. If the pressure of the mask against the patient's face is too great, the patients will be reluctant to use the mask. To counteract this deficiency, respiratory masks have been provided with seals of flexible, resilient material to soften and distribute the pressure of the mask against the face. While this has made the masks more comfortable, further improvements in comfort are needed.
Another aspect of respiratory masks is that means must be provided for adequate venting of the air exhaled by the patient. Without some type of venting, the exhaled air will merely accumulate in the mask or in the vent tube, with a resulting increase in the carbon dioxide level of the air supplied to the patient. Consequently, exit air ports for exhaled air are provided in most respiratory masks. For example, apertures in the mask body for the exhaled air of the patient are shown in U.S. Pat. No. 4,328,797. A problem with these exit air ports is that the rush of exhaled air generates noise and an air pulse which can disturb the patient or the patient's sleeping partner. An improved respiratory mask would provide for a quieter and less forceful exit of exhaled air.